Method and apparatus for establishing and/or monitoring the filling level of a medium in a container

Abstract

The invention relates to a method and an apparatus for establishing and/or monitoring the filling level of a medium in a container and to the determination of the density of a medium in a container. It is the object of the invention to propose a method and an apparatus which permit reliable determination and/or monitoring of the filling level or the density of a medium. With reference to the apparatus according to the invention, the object is achieved by virtue of the fact that at least a first mode and a second mode of the oscillations of the oscillable unit ( 2 ) are evaluated, and the evaluated modes are used to detect a change in mass at the oscillable unit ( 2 ).

What is claimed is:  
     
       1. A method for determining at least one of a filling level and a density of a medium in a container, the method comprising the steps of: 
       exciting an oscillable unit to oscillate by means of an exciter oscillation;  
       detecting that a predetermined filling level has been reached as soon as the oscillable unit oscillates at an oscillation frequency which exhibits a predetermined frequency change with respect to a frequency of the exciter oscillation;  
       determining the density of the medium with the aid of the oscillation frequency of the oscillable unit; and  
       evaluating at least a first mode and a second mode of the oscillations of the oscillable unit which exist while the oscillable unit is in contact with the medium to detect a change in mass at the oscillable unit.  
     
     
       2. The method as claimed in  claim 1 , wherein the evaluating step includes evaluating, as the first and second modes, modes whose oscillations are differently influenced by the medium. 
     
     
       3. The method as claimed in  claim 2 , wherein the first mode is a mode whose oscillations are essentially independent of the medium, and the second mode is a mode whose oscillations are essentially influenced by the medium. 
     
     
       4. The method as claimed in  claim 2 , wherein two modes are selected as first mode and as second mode of the oscillations of the oscillable unit ( 2 ), the two modes respectively having a first component which is a function of the medium, and the two modes having a second component which is essentially independent of the medium and depends essentially only on the respective mass of the oscillable unit ( 2 ). 
     
     
       5. The method as claimed in  claim 2 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       6. The method as claimed in  claim 2 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       7. The method as claimed in  claim 1 , wherein the first mode is a mode whose oscillations are essentially independent of the medium, and the second mode is a mode whose oscillations are essentially influenced by the medium. 
     
     
       8. The method as claimed in  claim 7 , wherein a change in the first mode whose oscillations are essentially independent of the medium is used to detect whether a change in mass has occurred at the oscillable unit ( 2 ). 
     
     
       9. The method as claimed in  claim 7 , wherein a change in frequency of the oscillations of the first mode is used to detect whether a change in mass has occurred at the oscillable unit ( 2 ). 
     
     
       10. The method as claimed in  claim 7 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       11. The method as claimed in  claim 7 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       12. The method as claimed in  claim 1 , wherein a change in the first mode whose oscillations are essentially independent of the medium is used to detect whether a change in mass has occurred at the oscillable unit ( 2 ). 
     
     
       13. The method as claimed in  claim 12 , wherein a change in frequency of the oscillations of the first mode is used to detect whether a change in mass has occurred at the oscillable unit ( 2 ). 
     
     
       14. The method as claimed in  claim 12 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       15. The method as claimed in  claim 12 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       16. The method as claimed in  claim 1 , wherein a change in frequency of the oscillations of the first mode is used to detect whether a change in mass has occurred at the oscillable unit ( 2 ). 
     
     
       17. The method as claimed in  claim 16 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       18. The method as claimed in  claim 16 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       19. The method as claimed in  claim 1 , wherein two modes are selected as first mode and as second mode of the oscillations of the oscillable unit ( 2 ), the two modes respectively having a first component which is a function of the medium, and the two modes having a second component which is essentially independent of the medium and depends essentially only on the respective mass of the oscillable unit ( 2 ). 
     
     
       20. The method as claimed in  claim 19 , further comprising the step of drawing conclusions on a mass of a coating which has formed on the oscillable unit, with the aid of a functional relationship of the first and second modes of the oscillations of the oscillable unit on the medium and on a mass of the oscillable unit. 
     
     
       21. The method as claimed in  claim 20 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       22. The method as claimed in  claim 20 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       23. The method as claimed in  claim 19 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       24. The method as claimed in  claim 19 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       25. The method as claimed in  claim 1 , further comprising the step of outputting an error message when changes in at least one of the first mode and the second mode of the oscillations of the oscillable unit, which changes are caused by the change in mass at the oscillable unit, overshoot a prescribed desired value. 
     
     
       26. The method as claimed in  claim 1 , further comprising the step of undertaking inline correction of the oscillation frequency of the oscillable unit based at least in part on a change, caused by a change in mass at the oscillable unit, in at least one of the first mode and the second mode of the oscillations of the oscillable unit. 
     
     
       27. An apparatus for determining at least one of a filling level and a density of a medium in a container, the apparatus comprising: 
       an oscillable unit which is configured to be fitted to the container;  
       a drive/reception unit which excites the oscillable unit to oscillate with the aid of a prescribed exciter frequency, and which receives oscillations of the oscillable unit; and  
       a control/evaluation unit which detects that a predetermined filling level has been reached as soon as a prescribed change in frequency occurs, and which determines the density of the medium with the aid of an oscillation frequency of the oscillable unit;  
       wherein the control/evaluation unit uses at least a first mode and a second mode of the oscillations of the oscillable unit which exist while the oscillable unit is in contact with the medium for the purpose of evaluation, and the control/evaluation unit detects a change in mass at the oscillable unit with the aid of the evaluated modes.  
     
     
       28. The apparatus as claimed in  claim 27 , wherein the evaluation/control unit is integrated into the apparatus for at least one of determining the filling level, monitoring the filling level , and determining the density of the medium. 
     
     
       29. The apparatus as claimed in  claim 28 , further comprising at least two data lines via which measured data are led to the evaluation/control unit. 
     
     
       30. The apparatus as claimed in  claim 28 , wherein an output unit ( 14 ) is provided which outputs an error message to the operating staff optically and/or acoustically when, preferably within the limits of prescribed tolerance values, a prescribed desired value of the change in frequency which is to be ascribed to a change in mass at the oscillable unit ( 2 ) is overshot or undershot. 
     
     
       31. The apparatus as claimed in  claim 27 , further comprising at least two data lines via which measured data are led to the evaluation/control unit. 
     
     
       32. The apparatus as claimed in  claim 31 , wherein the measured data and the data on the extent of the coating of the oscillable unit ( 2 ) are transmitted digitally to the remote control point ( 13 ). 
     
     
       33. The apparatus as claimed in  claim 31 , wherein an output unit ( 14 ) is provided which outputs an error message to the operating staff optically and/or acoustically when, preferably within the limits of prescribed tolerance values, a prescribed desired value of the change in frequency which is to be ascribed to a change in mass at the oscillable unit ( 2 ) is overshot or undershot. 
     
     
       34. The apparatus as claimed in  claim 27 , further comprising an output unit which outputs at least one of an optical error message and an acoustical error message to the operating staff when, preferably within the limits of prescribed tolerance values, a prescribed desired value of the change in frequency which is to be ascribed to a change in mass at the oscillable unit is at least one of overshot and undershot. 
     
     
       35. The apparatus as claimed in  claim 34 , wherein the control/evaluation unit ( 10 ) is assigned a storage unit ( 11 ) in which desired values are stored for tolerable changes in frequency which originate from a change in mass at the oscillable unit ( 2 ). 
     
     
       36. The apparatus as claimed in  claim 27 , wherein the control/evaluation unit ( 10 ) is assigned a storage unit ( 11 ) in which desired values are stored for tolerable changes in frequency which originate from a change in mass at the oscillable unit ( 2 ). 
     
     
       37. The apparatus as claimed in  claim 10 , further comprising at least two data lines via which the evaluation/control unit communicates with a remote control point. 
     
     
       38. The apparatus as claimed in  claim 11 , further comprising at least two data lines via which the evaluation/control unit communicates with a remote control point.